A prior art fuel cell electricity-generating device will be described hereinafter.
As shown in FIG. 9, a prior art fuel cell electricity-generating device has a fuel cell 1 of generating electricity with a fuel gas and an oxidizer, a fuel processor 2 of producing a fuel rich in hydrogen from an electricity-generating material comprising water incorporated in a natural gas or the like, a combustion device 3 of combusting a residual fuel gas discharged from the fuel cell 1, a blower 4 of supplying air into the fuel cell 1 as an oxidizer, an electric power generation instructing means 5 of adjusting the electric power generated by the fuel cell 1 and an electricity-generating material adjusting device 6 of adjusting the amount of electricity-generating material and water to be supplied into the fuel processor 2.
The fuel processor 2 comprises a fuel producing means of producing a fuel to be supplied into the fuel cell 1 and a carbon oxide removing means of reducing the content of carbon monoxide in the fuel gas to an extent such that the catalyst of the fuel cell 1 is not damaged.
The combustion device 3 receives the residual fuel gas discharged from the fuel cell 1 and combusts the residual fuel gas to raise the temperature of the fuel producing means of the fuel processor 2 to a temperature at which the fuel producing means of the fuel processor 2 can efficiently produce a fuel gas (about 700° C.).
The electricity-generating material adjusting device 6 adjusts the amount of the electricity-generating material to be supplied into the fuel processor 2 so that the fuel gas can be supplied into the fuel cell 1 in an amount required to generate the electric power determined by the electric power generation instructing means 5.
The electricity-generating material adjusting device 6 also adjusts the temperature of the fuel processor 2 by changing the amount of the electricity-generating material to be supplied into the fuel processor 2. When the temperature of the fuel processor 2 is raised, the amount of the electricity-generating material to be supplied into the fuel processor 2 is reduced to reduce the amount of the residual fuel gas to be supplied into the combustion device 3 and hence the amount of combustion in the combustion device 3 is reduced, thereby lowering the temperature of the fuel processor 2.
On the contrary, when the temperature of the fuel processor 2 is lowered, the electricity-generating material adjusting device 6 increases the amount of the electricity-generating material to be supplied into the fuel processor 2 to increase the amount of the residual fuel gas to be supplied into the combustion device 3 and hence the amount of combustion in the combustion device 3 is increased, thereby raising the temperature of the fuel processor 2.
In a fuel cell electricity-generating device such as the aforementioned prior art example, the carbon monoxide removing means provided in the fuel processor 2 performs effectively its function of removing carbon monoxide normally at from about 200° C. to about 300° C. In other words, the fuel processor 2 comprises in combination a fuel producing means which works at about 700° C. and a carbon monoxide removing means which works at from about 200° C. to about 300° C. and thus avoids sudden change of the supplied amount of the electricity-generating material so that the temperature of the two means are well balanced.
On the other hand, the electric power generation instructing means 5 changes the generated electric power successively depending on the load power to be supplied by the fuel cell electricity-generating device. Since the load power changes momentarily, it is desirable that the change of the supplied amount of the electricity-generating material be at the same time as the change of the load power to effect efficient generation of electricity.
Referring thus to a realistic method of supplying the electricity-generating material, when it is desired to raise the generated electric power, the generated electric power is raised at the same rate as that at which the amount of the electricity-generating material to be supplied into the fuel processor 2 is raised at a maximum rate at which the amount of the electricity-generating material can be raised (about 20 minutes needed to reach from 50% of rated output to rated output) because when the electricity-generating material runs short, the generated electric power cannot be raised.
On the other hand, when it is desired to lower the generated electric power, a process is employed which comprises suddenly lowering the generated electric power so that the amount of the residual fuel gas to be discharged from the fuel cell is transiently increased, and then decreasing the supplied amount of the electricity-generating material.
However, when the generated electric power is suddenly decreased to increase the amount of the residual fuel gas to be discharged from the fuel cell as mentioned above, the residual fuel gas is then supplied into the combustion device 3 to suddenly increase the amount of combustion in the combustion device 3 in a short period of time, causing abnormal rise of the temperature of the fuel processor 2 that makes it necessary that the operation of the fuel cell electricity-generating device be suspended. This not only deteriorates the durability of the fuel processor 2 but also leads to the damage of the fuel processor 2 in the worst case.